It's Good, But It's Not A Win

In 1973, the Supreme Court held that police officers did not need a
warrant to look inside a pack of cigarettes that they found in the coat
pocket of a man who had been arrested. Those kinds of warrantless
searches were allowed, the Court reasoned back then, to protect police
officers and to prevent the destruction of evidence.

Forty years later, California and the federal government urged the
Supreme Court to adopt the same rule for cellphones. Once someone is
arrested, they contended, police should be able to go through the entire
contents of his phone without a warrant because cellphones are just
like any other item that you can carry in your hand or pocket. But
today the Supreme Court emphatically rejected that argument. Therefore,
unless it’s an emergency, police need to get a warrant before they can
search your cellphone.

I'm sure this has something to do with that whole "secure in their persons, houses, papers, and effects, against unreasonable searches" thing in the 4th Amendment.